1. Field of the Invention
The invention relates to a method of testing reed contacts for poorly conductive surface contamination, the electrically conductive contact reeds thereof consisting of magnetostrictive material and being arranged in an hermetically closed envelope, the reed contact being closed in the magnetic field of a coil. A test current which varies as a function of the time is conducted through the closed reed contact while an excitation current is conducted through the coil to hold the contact closed, a voltage generated between ends of the reed contact by the test current being measured for some time and compared with a reference voltage. Further, the invention relates to a device for performing said method.
Surface contamination is to be understood to include dirt and dust particles, and other materials which are poor electrical conductors, and also oxide skins and insulating layers which may be present on the contact surface after the manufacture of reed contacts.
2. Description of the Prior Art
A method and a device of the kind set forth are described in U.S. Pat. No. 3,586,961. As disclosed in that patent, the contact pressure counteracts the torsional movement of the reeds which is caused by magnetostriction. The surface which is tested during the torsional movement is limited. Even though the contact pressure is chosen to be as low as possible, because of the spread in the rigidity of the various contacts the contact pressure must still be chosen so high that the torsional movement is substantially counteracted. Use of a time-varying coil flux is not advantageous either, because this causes a changing contact pressure and hence a changing contact resistance. It is a logical consequence thereof that for appropriate acceptance/rejection of a reed contact accurate control of the detection signal, and hence comparatively expensive equipment, is required.
The surface examined could be increased by increasing the current which is conducted through the reed contact. However, this surface is limited because of the magnetostrictive properties of the reed contact.